Variable valve actuation system configurations

ABSTRACT

Valve actuation systems are disclosed herein that allow valve closing timing to be varied using a lost-motion system. In some embodiments, an actuation system is provided that has a locked configuration in which a bearing element is held in place between first and second valve train components to transmit cam motion to an engine valve. The actuation system also has an unlocked configuration in which the bearing element is permitted to be at least partially ejected from between the first and second valve train components, such that cam motion is not transmitted to the engine valve. A number of valve train configurations are disclosed, including a pushrod with a translating follower, a pushrod with an end-pivoted follower, a center-pivoted rocker, an end-pivoted rocker, and a direct attack valve train with a bucket tappet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/679,123, filed on Aug. 3, 2012, the entire contents of which are hereby incorporated by reference.

FIELD

The present invention relates to internal combustion engines. More particularly, the invention relates to lost-motion variable valve actuation systems for internal combustion engines.

BACKGROUND

For purposes of clarity, the term “conventional engine” as used in the present application refers to an internal combustion engine wherein all four strokes of the well-known Otto cycle (the intake, compression, expansion and exhaust strokes) are contained in each piston/cylinder combination of the engine. Each stroke requires one half revolution of the crankshaft (180 degrees crank angle (“CA”)), and two full revolutions of the crankshaft (720 degrees CA) are required to complete the entire Otto cycle in each cylinder of a conventional engine.

Also, for purposes of clarity, the following definition is offered for the term “split-cycle engine” as may be applied to engines disclosed in the prior art and as referred to in the present application.

A split-cycle engine generally comprises:

a crankshaft rotatable about a crankshaft axis;

a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke during a single rotation of the crankshaft;

an expansion (power) piston slidably received within an expansion cylinder and operatively connected to the crankshaft such that the expansion piston reciprocates through an expansion stroke and an exhaust stroke during a single rotation of the crankshaft; and

a crossover passage interconnecting the compression and expansion cylinders, the crossover passage including at least a crossover expansion (XovrE) valve disposed therein, but more preferably including a crossover compression (XovrC) valve and a crossover expansion (XovrE) valve defining a pressure chamber therebetween.

A split-cycle air hybrid engine combines a split-cycle engine with an air reservoir (also commonly referred to as an air tank) and various controls. This combination enables the engine to store energy in the form of compressed air in the air reservoir. The compressed air in the air reservoir is later used in the expansion cylinder to power the crankshaft. In general, a split-cycle air hybrid engine as referred to herein comprises:

a crankshaft rotatable about a crankshaft axis;

a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke during a single rotation of the crankshaft;

an expansion (power) piston slidably received within an expansion cylinder and operatively connected to the crankshaft such that the expansion piston reciprocates through an expansion stroke and an exhaust stroke during a single rotation of the crankshaft;

a crossover passage (port) interconnecting the compression and expansion cylinders, the crossover passage including at least a crossover expansion (XovrE) valve disposed therein, but more preferably including a crossover compression (XovrC) valve and a crossover expansion (XovrE) valve defining a pressure chamber therebetween; and

an air reservoir operatively connected to the crossover passage and selectively operable to store compressed air from the compression cylinder and to deliver compressed air to the expansion cylinder.

FIG. 1 illustrates one exemplary embodiment of a prior art split-cycle air hybrid engine. The split-cycle engine 100 replaces two adjacent cylinders of a conventional engine with a combination of one compression cylinder 102 and one expansion cylinder 104. The compression cylinder 102 and the expansion cylinder 104 are formed in an engine block in which a crankshaft 106 is rotatably mounted. Upper ends of the cylinders 102, 104 are closed by a cylinder head 130. The crankshaft 106 includes axially displaced and angularly offset first and second crank throws 126, 128, having a phase angle therebetween. The first crank throw 126 is pivotally joined by a first connecting rod 138 to a compression piston 110, and the second crank throw 128 is pivotally joined by a second connecting rod 140 to an expansion piston 120 to reciprocate the pistons 110, 120 in their respective cylinders 102, 104 in a timed relation determined by the angular offset of the crank throws and the geometric relationships of the cylinders, crank, and pistons. Alternative mechanisms for relating the motion and timing of the pistons can be utilized if desired. The rotational direction of the crankshaft and the relative motions of the pistons near their bottom dead center (BDC) positions are indicated by the arrows associated in the drawings with their corresponding components.

The four strokes of the Otto cycle are thus “split” over the two cylinders 102 and 104 such that the compression cylinder 102 contains the intake and compression strokes and the expansion cylinder 104 contains the expansion and exhaust strokes. The Otto cycle is therefore completed in these two cylinders 102, 104 once per crankshaft 106 revolution (360 degrees CA).

During the intake stroke, intake air is drawn into the compression cylinder 102 through an inwardly-opening (opening inward into the cylinder and toward the piston) poppet intake valve 108. During the compression stroke, the compression piston 110 pressurizes the air charge and drives the air charge through a crossover passage 112, which acts as the intake passage for the expansion cylinder 104. The engine 100 can have one or more crossover passages 112.

The geometric compression ratio of the compression cylinder 102 of the split-cycle engine 100 (and for split-cycle engines in general) is herein referred to as the “compression ratio” of the split-cycle engine. The geometric compression ratio of the expansion cylinder 104 of the engine 100 (and for split-cycle engines in general) is herein referred to as the “expansion ratio” of the split-cycle engine. The geometric compression ratio of a cylinder is well known in the art as the ratio of the enclosed (or trapped) volume in the cylinder (including all recesses) when a piston reciprocating therein is at its BDC position to the enclosed volume (i.e., clearance volume) in the cylinder when said piston is at its top dead center (TDC) position. Specifically for split-cycle engines as defined herein, the compression ratio of a compression cylinder is determined when the XovrC valve is closed. Also specifically for split-cycle engines as defined herein, the expansion ratio of an expansion cylinder is determined when the XovrE valve is closed.

Due to very high geometric compression ratios (e.g., 20 to 1, 30 to 1, 40 to 1, or greater) within the compression cylinder 102, an outwardly-opening (opening outwardly away from the cylinder and piston) poppet crossover compression (XovrC) valve 114 at the inlet of the crossover passage 112 is used to control flow from the compression cylinder 102 into the crossover passage 112. Due to very high geometric compression ratios (e.g., 20 to 1, 30 to 1, 40 to 1, or greater) within the expansion cylinder 104, an outwardly-opening poppet crossover expansion (XovrE) valve 116 at the outlet of the crossover passage 112 controls flow from the crossover passage 112 into the expansion cylinder 104. The actuation rates and phasing of the XovrC and XovrE valves 114, 116 are timed to maintain pressure in the crossover passage 112 at a high minimum pressure (typically 20 bar or higher at full load) during all four strokes of the Otto cycle.

At least one fuel injector 118 injects fuel into the pressurized air at the exit end of the crossover passage 112 in coordination with the XovrE valve 116 opening. Alternatively, or in addition, fuel can be injected directly into the expansion cylinder 104. The fuel-air charge fully enters the expansion cylinder 104 shortly after the expansion piston 120 reaches its TDC position. As the piston 120 begins its descent from its TDC position, and while the XovrE valve 116 is still open, one or more spark plugs 122 are fired to initiate combustion (typically between 10 to 20 degrees CA after TDC of the expansion piston 120). Combustion can be initiated while the expansion piston is between 1 and 30 degrees CA past its TDC position. More preferably, combustion can be initiated while the expansion piston is between 5 and 25 degrees CA past its TDC position. Most preferably, combustion can be initiated while the expansion piston is between 10 and 20 degrees CA past its TDC position. Additionally, combustion can be initiated through other ignition devices and/or methods, such as with glow plugs, microwave ignition devices, or through compression ignition methods.

The XovrE valve 116 is then closed before the resulting combustion event enters the crossover passage 112. The combustion event drives the expansion piston 120 downward in a power stroke. Exhaust gases are pumped out of the expansion cylinder 104 through an inwardly-opening poppet exhaust valve 124 during the exhaust stroke.

With the split-cycle engine concept, the geometric engine parameters (i.e., bore, stroke, connecting rod length, compression ratio, etc.) of the compression and expansion cylinders are generally independent from one another. For example, the crank throws 126, 128 for the compression cylinder 102 and expansion cylinder 104, respectively, have different radii and are phased apart from one another with TDC of the expansion piston 120 occurring prior to TDC of the compression piston 110. This independence enables the split-cycle engine to potentially achieve higher efficiency levels and greater torques than typical four-stroke engines.

The geometric independence of engine parameters in the split-cycle engine 100 is also one of the main reasons why pressure can be maintained in the crossover passage 112 as discussed earlier. Specifically, the expansion piston 120 reaches its TDC position prior to the compression piston 110 reaching its TDC position by a discrete phase angle (typically between 10 and 30 crank angle degrees). This phase angle, together with proper timing of the XovrC valve 114 and the XovrE valve 116, enables the split-cycle engine 100 to maintain pressure in the crossover passage 112 at a high minimum pressure (typically 20 bar absolute or higher during full load operation) during all four strokes of its pressure/volume cycle. That is, the split-cycle engine 100 is operable to time the XovrC valve 114 and the XovrE valve 116 such that the XovrC and XovrE valves 114, 116 are both open for a substantial period of time (or period of crankshaft rotation) during which the expansion piston 120 descends from its TDC position towards its BDC position and the compression piston 110 simultaneously ascends from its BDC position towards its TDC position. During the period of time (or crankshaft rotation) that the crossover valves 114, 116 are both open, a substantially equal mass of gas is transferred (1) from the compression cylinder 102 into the crossover passage 112 and (2) from the crossover passage 112 to the expansion cylinder 104. Accordingly, during this period, the pressure in the crossover passage is prevented from dropping below a predetermined minimum pressure (typically 20, 30, or 40 bar absolute during full load operation). Moreover, during a substantial portion of the intake and exhaust strokes (typically 80% of the entire intake and exhaust strokes or greater), the XovrC valve 114 and XovrE valve 116 are both closed to maintain the mass of trapped gas in the crossover passage 112 at a substantially constant level. As a result, the pressure in the crossover passage 112 is maintained at a predetermined minimum pressure during all four strokes of the engine's pressure/volume cycle.

For purposes herein, the method of opening the XovrC 114 and XovrE 116 valves while the expansion piston 120 is descending from TDC and the compression piston 110 is ascending toward TDC in order to simultaneously transfer a substantially equal mass of gas into and out of the crossover passage 112 is referred to as the “push-pull” method of gas transfer. It is the push-pull method that enables the pressure in the crossover passage 112 of the engine 100 to be maintained at typically 20 bar or higher during all four strokes of the engine's cycle when the engine is operating at full load.

The crossover valves 114, 116 are actuated by a valve train that includes one or more cams (not shown). In general, a cam-driven mechanism includes a camshaft mechanically linked to the crankshaft. One or more cams are mounted to the camshaft, each having a contoured surface that controls the valve lift profile of the valve event (i.e., the event that occurs during a valve actuation). The XovrC valve 114 and the XovrE valve 116 each can have its own respective cam and/or its own respective camshaft. As the XovrC and XovrE cams rotate, actuating portions thereof impart motion to a rocker arm, which in turn imparts motion to the valve, thereby lifting (opening) the valve off of its valve seat. As the cam continues to rotate, the actuating portion passes the rocker arm and the valve is allowed to close.

The split-cycle air hybrid engine 100 also includes an air reservoir (tank) 142, which is operatively connected to the crossover passage 112 by an air reservoir tank valve 152. Embodiments with two or more crossover passages 112 may include a tank valve 152 for each crossover passage 112 which connects to a common air reservoir 142, may include a single valve which connects all crossover passages 112 to a common air reservoir 142, or each crossover passage 112 may operatively connect to separate air reservoirs 142.

The tank valve 152 is typically disposed in an air tank port 154, which extends from the crossover passage 112 to the air tank 142. The air tank port 154 is divided into a first air tank port section 156 and a second air tank port section 158. The first air tank port section 156 connects the air tank valve 152 to the crossover passage 112, and the second air tank port section 158 connects the air tank valve 152 to the air tank 142. The volume of the first air tank port section 156 includes the volume of all additional recesses which connect the tank valve 152 to the crossover passage 112 when the tank valve 152 is closed. Preferably, the volume of the first air tank port section 156 is small relative to the second air tank port section 158. More preferably, the first air tank port section 156 is substantially non-existent, that is, the tank valve 152 is most preferably disposed such that it is flush against the outer wall of the crossover passage 112.

The tank valve 152 may be any suitable valve device or system. For example, the tank valve 152 may be an active valve which is activated by various valve actuation devices (e.g., pneumatic, hydraulic, cam, electric, or the like). Additionally, the tank valve 152 may comprise a tank valve system with two or more valves actuated with two or more actuation devices.

The air tank 142 is utilized to store energy in the form of compressed air and to later use that compressed air to power the crankshaft 106. This mechanical means for storing potential energy provides numerous potential advantages over the current state of the art. For instance, the split-cycle air hybrid engine 100 can potentially provide many advantages in fuel efficiency gains and NOx emissions reduction at relatively low manufacturing and waste disposal costs in relation to other technologies on the market, such as diesel engines and electric-hybrid systems.

The engine 100 typically runs in a normal operating or firing (NF) mode (also commonly called the engine firing (EF) mode) and one or more of four basic air hybrid modes. In the NF mode, the engine 100 functions normally as previously described in detail herein, operating without the use of the air tank 142. In the NF mode, the air tank valve 152 remains closed to isolate the air tank 142 from the basic split-cycle engine. In the four air hybrid modes, the engine 100 operates with the use of the air tank 142.

The four basic air hybrid modes include:

1) Air Expander (AE) mode, which includes using compressed air energy from the air tank 142 without combustion;

2) Air Compressor (AC) mode, which includes storing compressed air energy into the air tank 142 without combustion;

3) Air Expander and Firing (AEF) mode, which includes using compressed air energy from the air tank 142 with combustion; and

4) Firing and Charging (FC) mode, which includes storing compressed air energy into the air tank 142 with combustion.

Further details on split-cycle engines can be found in U.S. Pat. No. 6,543,225 entitled Split Four Stroke Cycle Internal Combustion Engine and issued on Apr. 8, 2003; and U.S. Pat. No. 6,952,923 entitled Split-Cycle Four-Stroke Engine and issued on Oct. 11, 2005, each of which is incorporated by reference herein in its entirety.

Further details on air hybrid engines are disclosed in U.S. Pat. No. 7,353,786 entitled Split-Cycle Air Hybrid Engine and issued on Apr. 8, 2008; U.S. Patent Application No. 61/365,343 entitled Split-Cycle Air Hybrid Engine and filed on Jul. 18, 2010; and U.S. Patent Application No. 61/313,831 entitled Split-Cycle Air Hybrid Engine and filed on Mar. 15, 2010, each of which is incorporated by reference herein in its entirety.

A number of valve actuation systems are disclosed in U.S. Publication No. 2013/0152889 entitled “LOST-MOTION VARIABLE VALVE ACTUATION SYSTEM” and published on Jun. 20, 2013, the entire contents of which are hereby incorporated by reference herein.

SUMMARY

Valve actuation systems are disclosed herein that allow valve closing timing to be varied using a lost-motion system. In some embodiments, an actuation system is provided that has a locked configuration in which a bearing element is held in place between first and second valve train components to transmit cam motion to an engine valve. The actuation system also has an unlocked configuration in which the bearing element is permitted to be at least partially ejected from between the first and second valve train components, such that cam motion is not transmitted to the engine valve. A number of valve train configurations are disclosed, including a pushrod with a translating follower, a pushrod with an end-pivoted follower, a center-pivoted rocker, an end-pivoted rocker, and a direct attack valve train with a bucket tappet.

In one aspect of at least one embodiment of the invention, a lost-motion variable valve actuation system is provided that includes a rocker arm having a first rocker pad that engages an engine valve and a second rocker pad, a pushrod having a first end in engagement with the second rocker pad and a second end in engagement with a follower, and an actuation system configured to selectively permit a bearing element to be at least partially ejected from between the follower and a cam to allow the engine valve to close.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the follower comprises a cylindrical canister with a closed end that defines a contact surface that engages the bearing element.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the follower is configured to rotate about an axis of rotation and wherein the follower comprises a first end having a bore formed therein through which a shaft extends along the axis of rotation and a second end opposite the first end that engages the bearing element.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the second end comprises a roller rotatably mounted therein such that the roller engages the bearing element.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the second end of the pushrod engages the follower at a location intermediate to the first and second ends of the follower.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the pushrod is coupled to the follower by a ball and socket coupling.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the engine valve is inwardly-opening.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the actuation system has a locked configuration in which the bearing element is maintained between the follower and the cam and an unlocked configuration in which the bearing element can be at least partially ejected from between the follower and the cam.

In another aspect of at least one embodiment of the invention, a lost-motion variable valve actuation system is provided that includes a rocker arm having a first rocker pad that engages an engine valve and a second rocker pad, and an actuation system configured to selectively permit a bearing element to be at least partially ejected from between the second rocker pad and a cam to allow the engine valve to close. The rocker arm is configured to rotate about an axis of rotation.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the first and second rocker pads are formed at opposed ends of the rocker arm and wherein the axis of rotation is disposed intermediate to the first and second rocker pads.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the axis of rotation is disposed at a first end of the rocker arm, the first rocker pad is formed at a second, opposite end of the rocker arm, and the second rocker pad is formed at a location intermediate to the first and second ends of the rocker arm.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the second rocker pad comprises a roller rotatably mounted in the rocker arm.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the engine valve is inwardly-opening.

Related aspects of at least one embodiment of the invention provide a system, e.g., as described above, in which the actuation system has a locked configuration in which the bearing element is maintained between the rocker arm and the cam and an unlocked configuration in which the bearing element can be at least partially ejected from between the rocker arm and the cam.

The present invention further provides devices, systems, and methods as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic sectional view of a prior art air hybrid split-cycle engine;

FIG. 2A is a schematic view of one embodiment of a valve train in which a valve is closed;

FIG. 2B is a schematic view of the valve train of FIG. 2A in which the valve is opened;

FIG. 2C is a schematic view of the valve train of FIGS. 2A and 2B in which the valve is closed earlier than what is called for by a profile of a cam;

FIG. 3 is a schematic sectional view of an exemplary embodiment of an actuation system and bearing element;

FIG. 4 is a schematic view of an exemplary embodiment of a pushrod valve train with a translating follower;

FIG. 5 is a schematic view of an exemplary embodiment of a pushrod valve train with an end-pivoted follower;

FIG. 6 is a schematic view of an exemplary embodiment of a valve train with a center-pivoted rocker;

FIG. 7 is a schematic view of an exemplary embodiment of a valve train with an end-pivoted rocker; and

FIG. 8 is a schematic view of an exemplary embodiment of a direct attack valve train with a bucket tappet.

DETAILED DESCRIPTION

Valve actuation systems are disclosed herein that allow valve closing timing to be varied using a lost-motion system. In some embodiments, an actuation system is provided that has a locked configuration in which a bearing element is held in place between first and second valve train components to transmit cam motion to an engine valve. The actuation system also has an unlocked configuration in which the bearing element is permitted to be at least partially ejected from between the first and second valve train components, such that cam motion is not transmitted to the engine valve. A number of valve train configurations are disclosed, including a pushrod with a translating follower, a pushrod with an end-pivoted follower, a center-pivoted rocker, an end-pivoted rocker, and a direct attack valve train with a bucket tappet.

Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the methods, systems, and devices disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the methods, systems, and devices specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.

Although certain methods and devices are disclosed herein in the context of a split-cycle engine and/or an air hybrid engine, a person having ordinary skill in the art will appreciate that the methods and devices disclosed herein can be used in any of a variety of contexts, including, without limitation, non-hybrid engines, two-stroke and four-stroke engines, conventional engines, natural gas engines, diesel engines, etc.

FIGS. 2A-2C illustrate one exemplary embodiment of a valve train 200 suitable for adjusting the opening and closing timing of an engine valve (e.g., by modifying the valve motion proscribed by a cam profile). The illustrated valve train 200 can be used to actuate any of the valves of the engine 100 described above including without limitation the XovrC and XovrE crossover valves. For purposes herein, a valve train of an internal combustion engine is defined as a system of valve train elements, which are used to control the actuation of the valves. The valve train elements generally comprise a combination of actuating elements and their associated support elements. The actuating elements (e.g., cams, tappets, springs, rocker arms, and the like) are used to directly impart the actuation motion to the valves (i.e., to actuate the valves) of the engine during each valve event. The support elements (e.g., shafts, pedestals, and the like) securely mount and guide the actuating elements.

As shown in FIG. 2A, the valve train 200 generally includes a cam 202, a rocker 204, a valve 206, and an adjustable mechanical element 208. The valve train 200 can also include one or more associated support elements, which for purposes of brevity are not illustrated.

The valve 206 includes a valve head 210 and a valve stem 212 extending vertically from the valve head 210. A valve adapter assembly 214 is disposed at the tip of the stem 212 opposite the head 210 and is securely fixed thereto. A valve spring (not shown) holds the valve head 210 securely against a valve seat 216 when the valve 206 is in its closed position. Any of a variety of valve springs can be used for this purpose, including, for example, air or gas springs. In addition, although the illustrated valve 206 is an outwardly-opening poppet valve, any cam actuated valve can be used, including inwardly-opening poppet valves, without departing from the scope of the present invention.

The rocker 204 includes a forked rocker pad 220 at one end, which straddles the valve stem 212 and engages the underside of the valve adapter assembly 214. Additionally, the rocker 204 includes a solid rocker pad 222 at an opposing end, which slidably contacts the adjustable mechanical element 208. The rocker 204 also includes a rocker shaft bore 224 extending therethrough. The rocker shaft bore 224 is disposed over a supporting rocker shaft 228 such that the rocker 204 rotates on the rocker shaft 228 about an axis of rotation 229. Either of the rocker pads 220, 222 can include one or more rollers. One or more roller bearings can also be provided in the rocker shaft bore 224, where the rocker 204 articulates relative to the rocker shaft 228.

The forked rocker pad 220 of the rocker 204 contacts the valve adapter assembly 214 of the outwardly-opening poppet valve 206 such that a downward direction of the rocker pad 222 caused by the actuation of the cam 202 and adjustable mechanical element 208 translates into an upward movement of the rocker pad 220, which in turn opens the valve 206. The geometry of the rocker 204 is selected to achieve a desired ratio of the distance between the forked rocker pad 220 and the axis of the rocker rotation 229 to the distance between the rocker pad 222 and the axis of rocker rotation 229. In one embodiment, this ratio can be between about 1:1 and about 2:1, and preferably about 1.3:1, about 1.4:1, about 1.5:1, about 1.6:1, or about 1.7:1. In addition, the ratio between the peak valve lift and the peak cam lift, which can dictate the diameter of the cam lobe base circle and the cam concavity, can have any of a variety of values. In exemplary embodiments, the ratio between the peak valve lift and the peak cam lift is between about 1.0:1 and about 2.0:1, e.g., about 1.3:1, about 1.5:1, etc.

The cam 202 is a “dwell cam,” which as used herein is a cam that includes a dwell section (i.e., a section of the actuating portion of the cam having a constant cam lift) of at least 1 degree CA, and preferably at least 5 degrees CA. In the illustrated embodiment, the dwell cam 202 rotates clockwise (in the direction of the arrow A1). The dwell cam 202 generally includes a base circle portion 218 and an actuating portion 226. As the actuating portion 226 of the cam 202 contacts the adjustable mechanical element 208, the adjustable mechanical element pivots, which then causes the rocker 204 to rotate about the rocker shaft 228 to lift the valve 206 off of its seat 216.

The actuating portion 226 comprises an opening ramp 230, a closing ramp 232, and a dwell section 234. The dwell section 234 can be of various sizes, (i.e., at least 1 degree CA or at least 5 degrees CA) and in the illustrated embodiment, is sized to match the longest possible valve event duration (i.e., maximum valve event) needed over a full range of engine operating conditions and/or air hybrid modes. The opening ramp 230 of the cam 202 is contoured to a shape that adequately achieves the desired lift of the engine valve 206 at the desired rate. The closing ramp 232 (or “refill” ramp) is shaped to control the refill rate of a hydraulic actuation system 300. Further detail on dwell cams can be found in U.S. Publication No. 2012/0192841, published on Aug. 2, 2012, entitled “SPLIT-CYCLE AIR HYBRID ENGINE WITH DWELL CAM,” the entire contents of which are incorporated herein by reference.

The opening timing of the valve 206 can be adjusted by changing the timing within a given engine cycle at which the opening ramp 230 of the cam 202 contacts the adjustable mechanical element 208. In an exemplary embodiment, this is accomplished using a cam phaser which is configured to selectively alter the rotational position of the cam 202 relative to the rotational position of the engine's crankshaft. Further detail on cam phasers and their use to adjust the opening timing of an engine valve can be found in U.S. Publication No. 2012/0192818, published on Aug. 2, 2012, entitled “LOST-MOTION VARIABLE VALVE ACTUATION SYSTEM WITH CAM PHASER,” the entire contents of which are incorporated herein by reference.

The closing timing of the valve 206 can be controlled using the adjustable mechanical element 208. In the embodiment of FIGS. 2A-2C, the adjustable mechanical element 208 includes a bearing element 236, a connecting arm 238, and an actuation system 300.

As shown, the bearing element 236 has a generally elliptical-shaped cross-section defined by opposed first and second bearing surfaces 242, 244, each having a generally convex profile. It will be appreciated that other configurations are also possible, as described in U.S. Publication No. 2013/0152889 entitled “LOST-MOTION VARIABLE VALVE ACTUATION SYSTEM” and published on Jun. 20, 2013. The bearing element 236 is selectively positioned between the cam 202 and the rocker 204 such that the first bearing surface 242 slidably engages the cam 202 and the second bearing surface 244 slidably engages the rocker pad 222. The bearing element 236 can have one or more cavities 246 formed therein, for example to reduce the overall mass of the bearing element 236 and thus facilitate faster actuation.

The bearing element 236 is coupled to the actuation system 300 via the connecting arm 238, which can be formed integrally with the bearing element 236 or can be coupled thereto by a rotation joint that permits rotation of the bearing element 236 about one or more axes relative to the connecting arm 238. The proximal end 248 of the connecting arm 238 can be mated to the actuation system 300 in a variety of ways. Preferably, the proximal end 248 of the connecting arm 238 is pivotable with respect to the actuation system 300. In other words, the connecting arm 238 is free to rotate about a rotational axis that is substantially transverse to a longitudinal axis of the actuation system 300. As described below, the actuation system 300 is configured to allow the position of the bearing element 236 relative to the cam 202 and rocker 204 to be adjusted.

In operation, the cam 202 rotates clockwise as a camshaft, to which it is mounted, is driven by rotation of the engine's crankshaft. As shown in FIG. 2A, when the base circle portion 218 of the cam 202 engages the bearing element 236, the rocker 204 remains in a “fully closed” position in which the forked rocker pad 220 is either not in contact with or does not apply sufficient lifting force to the valve 206 to overcome the bias of the valve spring, and therefore the valve 206 remains closed.

As shown in FIG. 2B, the actuating portion 226 of the cam 202 engages the first bearing surface 242 of the bearing element 236 during a portion of the cam's rotation. The actuating portion 226 imparts a downward motion to the bearing element 236, causing the connecting arm 238 to pivot in a clockwise direction relative to the actuation system 300. As the connecting arm 238 pivots, some or all of the downward motion of the bearing element 236 is imparted to the rocker 204, which engages the second bearing surface 244 of the bearing element 236. This results in a counterclockwise rotation of the rocker 204, which in turn is effective to lift the valve 206 off of the seat 216. In FIG. 2B, the actuation system 300 is in a “locked” configuration in which the connecting arm 238 and bearing element 236 are held between the cam 202 and rocker 204. In this configuration, some or all of the motion imparted to the bearing element 236 is transferred to the valve 206, lifting it off of the seat 216. In other words, with the actuation system 300 in the locked configuration, the motion of the valve 206 will substantially follow the profile of the cam 202 according to the geometry of the actuation elements of the valve train.

As shown in FIG. 2C, the valve train 200 is capable of closing the valve 206 before the closing ramp 232 of the cam 202, as the cam rotates, reaches the bearing element 236. For example, the actuation system 300 can be transitioned to an “unlocked” configuration in which the connecting arm 238 and bearing element 236 are allowed to move in the direction of the arrow A2. Such movement is encouraged by a squeezing force in the direction of the arrow A2, which pushes the bearing element 236 away from the cam 202 and the rocker 204. The squeezing force is generated by a combination of the force of the valve spring biasing the rocker arm 204 in a clockwise direction, the force of the cam's actuating portion 226 rotating against the bearing element 236 in a clockwise direction, and the net force imparted to the valve head 210 by fluid pressure within the engine cylinder or crossover passage. It will be appreciated that the squeezing force can be only a minor component of the force acting on the bearing element 236, and that the bearing element 236 can be shaped such that the majority of the force of the cam 202 is applied downwards onto the rocker pad 222 and vice versa.

As shown in FIG. 2C, when the actuation system 300 is unlocked, the bearing element 236 can be withdrawn far enough from the cam 202 and the rocker 204 such that insufficient motion is imparted from the actuating portion 226 of the cam 202 to the rocker 204 for the valve 206 to actually be lifted off of the seat 216, and thus the valve 206 closes or remains closed. The valve train 200 thus provides a lost-motion feature that allows for variable valve actuation (i.e., permits the valve 206 to close at an earlier time than that provided by the profile of the cam 202). The valve train 200 is therefore configured to transmit all of the cam motion to the valve 206, to transmit only a portion of the cam motion to the valve 206, or to transmit none of the cam motion to the valve 206.

The actuation system 300 can also be configured to take up any lash that may exist in the valve train 200, for example due to thermal expansion and contraction, component wear, etc. For purposes herein, the terms “valve lash” or “lash” are defined as the total clearance existing between the rocker pad 220 and the valve adapter assembly 214 when all of the other components of the valve train 200 are positioned in such a way as to have no other clearance other than the clearance between the rocker pad 220 and the valve adapter assembly 214 when the valve 206 is fully seated. The valve lash is equal to the total contribution of all the individual clearances between all individual valve train elements (i.e., actuating elements and support elements) of the valve train 200. In the valve train 200, the actuation system 300 biases the bearing element 236 towards the cam 202 and the rocker 204 such that any lash that may exist in the valve train 200 is taken up by the gradually increasing thickness of the bearing element 236. The biasing force can be relatively low, such that once the lash is taken up by the bearing element 236, the bearing element 236 is not advanced further towards the cam 202 or rocker 204. In this manner, the lash is taken up without the valve 206 opening during a period when it should be closed.

FIG. 3 shows an exemplary embodiment of an actuation system 300 and bearing element 236, the structure and operation of which is described in detail in U.S. Publication No. 2013/0152889 entitled “LOST-MOTION VARIABLE VALVE ACTUATION SYSTEM” and published on Jun. 20, 2013.

It will be appreciated that the arrangements of valve train components shown in the foregoing drawings are merely exemplary, and that any of a variety of arrangements can be used depending factors such as engine type, geometry, configuration, packaging, and so forth. FIGS. 4-8 schematically illustrate exemplary valve train arrangements for use with inwardly-opening valves.

Pushrod Valve Train with Translating Follower

FIG. 4 illustrates an exemplary embodiment of a pushrod valve train 400 with a translating follower. As shown, the valve train 400 generally includes a cam 402, a rocker 404, a valve 406, an adjustable mechanical element 408, a pushrod 450, and a translating follower 452. The adjustable mechanical element 408 includes an actuation system 454 and a bearing element 436. Except as indicated below or as will be apparent to one having ordinary skill in the art, the structure and operation of the components of the valve train 400 are substantially the same as the corresponding components of the valve train 200 described above.

The valve 406 includes a valve head 410 and a valve stem 412 extending vertically from the valve head 410. A valve spring (not shown) holds the valve head 410 securely against a valve seat (not shown) when the valve 406 is in its closed position. Any of a variety of valve springs can be used for this purpose, including, for example, air or gas springs. The valve is an inwardly-opening poppet valve, such that the valve opens by moving inward, towards the engine cylinder.

The rocker 404 includes a first rocker pad 420 at one end which contacts and bears against the valve stem 412. The rocker 404 also includes a second rocker pad 422 at an opposing end, which is coupled (e.g., via a ball and socket or other coupling) to the upper end of the push rod 450. The rocker 404 also includes a rocker shaft bore 424 extending therethrough. The rocker shaft bore 424 is disposed over a supporting rocker shaft 428 such that the rocker 404 rotates on the rocker shaft 428 about an axis of rotation 429. Either of the rocker pads 420, 422 can include one or more rollers. One or more roller bearings can also be provided in the rocker shaft bore 424, where the rocker 404 articulates relative to the rocker shaft 428.

The lower end of the push rod 450 is coupled (e.g., via a ball and socket or other coupling) to the follower 452. In the illustrated embodiment, the follower 452 is a hollow cylindrical canister that is closed at one end to define a bearing surface configured to engage the bearing element 436. The adjustable mechanical element 408 is positioned such that the bearing element 436 is disposed between the follower 452 and the cam 402.

In operation, the cam 402 rotates clockwise as a camshaft, to which it is mounted, is driven by rotation of the engine's crankshaft. When the base circle portion 418 of the cam 402 engages the bearing element 436, the rocker 404 remains in a “fully closed” position in which the rocker pad 420 is either not in contact with or does not apply sufficient opening force to the valve 406 to overcome the bias of the valve spring, and therefore the valve 406 remains closed.

The actuating portion 426 of the cam 402 engages the bearing element 436 during a portion of the cam's rotation. When the actuation system 454 is in a “locked” configuration, the actuating portion 426 imparts an upward motion to the bearing element 436, lifting the follower 452 and the pushrod 450 and imparting some or all of the upward motion to the rocker 404. This results in a clockwise rotation of the rocker 404, which in turn is effective to lift the valve 406 off of its seat. In other words, the bearing element 436 can be held between the cam 402 and follower 452 such that the motion of the valve 406 will substantially follow the profile of the cam 402 according to the geometry of the actuation elements of the valve train.

The valve 406 can be closed before the timing specified by the cam profile by transitioning the actuation system 454 to an “unlocked” configuration. In the unlocked configuration, the actuation system 454 allows the bearing element 436 to be at least partially ejected from between the cam 402 and the follower 454 by valve train forces. The bearing element 436 can be withdrawn far enough from the cam 402 and the follower 454 such that insufficient motion is imparted from the actuating portion 426 of the cam to the rocker 404 for the valve 406 to actually be lifted off of its seat, and thus the valve 406 closes or remains closed. The valve train 400 thus provides a lost-motion feature that allows for variable valve actuation (i.e., permits the valve 406 to close at an earlier time than that provided by the profile of the cam 402). The valve train 400 is therefore configured to transmit all of the cam motion to the valve 406, to transmit only a portion of the cam motion to the valve 406, or to transmit none of the cam motion to the valve 406.

Pushrod Valve Train with End-Pivoted Follower

FIG. 5 illustrates an exemplary embodiment of a pushrod valve train 500 with an end-pivoted follower. As shown, the valve train 500 generally includes a cam 502, a rocker 504, a valve 506, an adjustable mechanical element 508, a pushrod 550, and an end-pivoted follower 552. The adjustable mechanical element 508 includes an actuation system 554 and a bearing element 536. Except as indicated below or as will be apparent to one having ordinary skill in the art, the structure and operation of the components of the valve train 500 are substantially the same as the corresponding components of the valve train 200 described above.

The valve 506 includes a valve head 510 and a valve stem 512 extending vertically from the valve head 510. A valve spring (not shown) holds the valve head 510 securely against a valve seat (not shown) when the valve 506 is in its closed position. Any of a variety of valve springs can be used for this purpose, including, for example, air or gas springs. The valve is an inwardly-opening poppet valve, such that the valve opens by moving inward, towards the engine cylinder.

The rocker 504 includes a first rocker pad 520 at one end which contacts and bears against the valve stem 512. The rocker 504 also includes a second rocker pad 522 at an opposing end, which is coupled (e.g., via a ball and socket or other coupling) to the upper end of the push rod 550. The rocker 504 also includes a rocker shaft bore 524 extending therethrough. The rocker shaft bore 524 is disposed over a supporting rocker shaft 528 such that the rocker 504 rotates on the rocker shaft 528 about an axis of rotation 529. Either of the rocker pads 520, 522 can include one or more rollers. One or more roller bearings can also be provided in the rocker shaft bore 524, where the rocker 504 articulates relative to the rocker shaft 528.

The lower end of the push rod 550 is coupled (e.g., via a ball and socket or other coupling) to the follower 552. The follower 552 is configured to rotate or pivot about an axis of rotation 556. For example, the follower 552 can include a first end with a bore formed therein through which a shaft can extend such that the follower is rotatably mounted on the shaft. Alternatively, the follower can be fixedly coupled to the shaft and the shaft can in turn be rotatably mounted within a shaft support structure. A second, opposite end of the follower 552 engages the bearing element 536, optionally via a roller 558. The adjustable mechanical element 508 is positioned such that the bearing element 536 is disposed between the follower 552 and the cam 502.

In operation, the cam 502 rotates clockwise as a camshaft, to which it is mounted, is driven by rotation of the engine's crankshaft. When the base circle portion 518 of the cam 502 engages the bearing element 536, the rocker 504 remains in a “fully closed” position in which the rocker pad 520 is either not in contact with or does not apply sufficient opening force to the valve 506 to overcome the bias of the valve spring, and therefore the valve 506 remains closed.

The actuating portion 526 of the cam 502 engages the bearing element 536 during a portion of the cam's rotation. When the actuation system 554 is in a “locked” configuration, the actuating portion 526 imparts an upward motion to the bearing element 536, causing the follower 552 to rotate about its rotation axis in a clockwise direction, lifting the pushrod 550 and imparting some or all of the upward motion to the rocker 504. This results in a clockwise rotation of the rocker 504, which in turn is effective to lift the valve 506 off of its seat. In other words, the bearing element 536 can be held between the cam 502 and follower 552 such that the motion of the valve 506 will substantially follow the profile of the cam 502 according to the geometry of the actuation elements of the valve train.

The valve 506 can be closed before the timing specified by the cam profile by transitioning the actuation system 554 to an “unlocked” configuration. In the unlocked configuration, the actuation system 554 allows the bearing element 536 to be at least partially ejected from between the cam 502 and the follower 552 by valve train forces. The bearing element 536 can be withdrawn far enough from the cam 502 and the follower 552 such that insufficient motion is imparted from the actuating portion 526 of the cam to the rocker 504 for the valve 506 to actually be lifted off of its seat, and thus the valve 506 closes or remains closed. The valve train 500 thus provides a lost-motion feature that allows for variable valve actuation (i.e., permits the valve 506 to close at an earlier time than that provided by the profile of the cam 502). The valve train 500 is therefore configured to transmit all of the cam motion to the valve 506, to transmit only a portion of the cam motion to the valve 506, or to transmit none of the cam motion to the valve 506.

Center-Pivoted Rocker

FIG. 6 illustrates an exemplary embodiment of a valve train 600 with a center-pivoted rocker. As shown, the valve train 600 generally includes a cam 602, a rocker 604, a valve 606, and an adjustable mechanical element 608. The adjustable mechanical element 608 includes an actuation system 654 and a bearing element 636. Except as indicated below or as will be apparent to one having ordinary skill in the art, the structure and operation of the components of the valve train 600 are substantially the same as the corresponding components of the valve train 200 described above.

The valve 606 includes a valve head 610 and a valve stem 612 extending vertically from the valve head 610. A valve spring (not shown) holds the valve head 610 securely against a valve seat (not shown) when the valve 606 is in its closed position. Any of a variety of valve springs can be used for this purpose, including, for example, air or gas springs. The valve is an inwardly-opening poppet valve, such that the valve opens by moving inward, towards the engine cylinder.

The rocker 604 includes a first rocker pad 620 at one end which contacts and bears against the valve stem 612. The rocker 604 also includes a second rocker pad 622 at an opposing end, that engages the bearing element 636. The rocker 604 also includes a rocker shaft bore 624 extending therethrough. The rocker shaft bore 624 is disposed over a supporting rocker shaft 628 such that the rocker 604 rotates on the rocker shaft 628 about an axis of rotation 629. Either of the rocker pads 620, 622 can include one or more rollers (e.g., a roller 658 as shown). One or more roller bearings can also be provided in the rocker shaft bore 624, where the rocker 604 articulates relative to the rocker shaft 628. The adjustable mechanical element 608 is positioned such that the bearing element 636 is disposed between the rocker 604 and the cam 602.

In operation, the cam 602 rotates clockwise as a camshaft, to which it is mounted, is driven by rotation of the engine's crankshaft. When the base circle portion 618 of the cam 602 engages the bearing element 636, the rocker 604 remains in a “fully closed” position in which the rocker pad 620 is either not in contact with or does not apply sufficient opening force to the valve 606 to overcome the bias of the valve spring, and therefore the valve 606 remains closed.

The actuating portion 626 of the cam 602 engages the bearing element 636 during a portion of the cam's rotation. When the actuation system 654 is in a “locked” configuration, the actuating portion 626 imparts an upward motion to the bearing element 636, resulting in a clockwise rotation of the rocker 604, which in turn is effective to lift the valve 606 off of its seat. In other words, the bearing element 636 can be held between the cam 602 and rocker 604 such that the motion of the valve 606 will substantially follow the profile of the cam 602 according to the geometry of the actuation elements of the valve train.

The valve 606 can be closed before the timing specified by the cam profile by transitioning the actuation system 654 to an “unlocked” configuration. In the unlocked configuration, the actuation system 654 allows the bearing element 636 to be at least partially ejected from between the cam 602 and the rocker 604 by valve train forces. The bearing element 636 can be withdrawn far enough from the cam 602 and the rocker 604 such that insufficient motion is imparted from the actuating portion 626 of the cam to the rocker 604 for the valve 606 to actually be lifted off of its seat, and thus the valve 606 closes or remains closed. The valve train 600 thus provides a lost-motion feature that allows for variable valve actuation (i.e., permits the valve 606 to close at an earlier time than that provided by the profile of the cam 602). The valve train 600 is therefore configured to transmit all of the cam motion to the valve 606, to transmit only a portion of the cam motion to the valve 606, or to transmit none of the cam motion to the valve 606.

End-Pivoted Rocker

FIG. 7 illustrates an exemplary embodiment of a valve train 700 with an end-pivoted rocker. As shown, the valve train 700 generally includes a cam 702, a rocker 704, a valve 706, and an adjustable mechanical element 708. The adjustable mechanical element 708 includes an actuation system 754 and a bearing element 736. Except as indicated below or as will be apparent to one having ordinary skill in the art, the structure and operation of the components of the valve train 700 are substantially the same as the corresponding components of the valve train 200 described above.

The valve 706 includes a valve head 710 and a valve stem 712 extending vertically from the valve head 710. A valve spring (not shown) holds the valve head 710 securely against a valve seat (not shown) when the valve 706 is in its closed position. Any of a variety of valve springs can be used for this purpose, including, for example, air or gas springs. The valve is an inwardly-opening poppet valve, such that the valve opens by moving inward, towards the engine cylinder.

The rocker 704 is configured to rotate or pivot about an axis of rotation 756. For example, the rocker can include a first end with a bore formed therein through which a shaft can extend such that the rocker is rotatably mounted on the shaft. Alternatively, the follower can be fixedly coupled to the shaft and the shaft can in turn be rotatably mounted within a shaft support structure. A second, opposite end of the rocker 704 includes a first rocker pad 720 which contacts and bears against the valve stem 712. A second rocker pad 722 for engaging the bearing element 736 can be disposed intermediate to the first and second ends of the rocker 704 (e.g., approximately at the center of the rocker 704). In some embodiments, the second rocker pad 722 can be or can include a roller 758 rotatably mounted in the rocker 704. The adjustable mechanical element 708 is positioned such that the bearing element 736 is disposed between the rocker 704 and the cam 702.

In operation, the cam 702 rotates clockwise as a camshaft, to which it is mounted, is driven by rotation of the engine's crankshaft. When the base circle portion 718 of the cam 702 engages the bearing element 736, the rocker 704 remains in a “fully closed” position in which the rocker pad 720 is either not in contact with or does not apply sufficient opening force to the valve 706 to overcome the bias of the valve spring, and therefore the valve 706 remains closed.

The actuating portion 726 of the cam 702 engages the bearing element 736 during a portion of the cam's rotation. When the actuation system 754 is in a “locked” configuration, the actuating portion 726 imparts a downward motion to the bearing element 736, resulting in a clockwise rotation of the rocker 704, which in turn is effective to lift the valve 706 off of its seat. In other words, the bearing element 736 can be held between the cam 702 and rocker 704 such that the motion of the valve 706 will substantially follow the profile of the cam 702 according to the geometry of the actuation elements of the valve train.

The valve 706 can be closed before the timing specified by the cam profile by transitioning the actuation system 754 to an “unlocked” configuration. In the unlocked configuration, the actuation system 754 allows the bearing element 736 to be at least partially ejected from between the cam 702 and the rocker 704 by valve train forces. The bearing element 736 can be withdrawn far enough from the cam 702 and the rocker 704 such that insufficient motion is imparted from the actuating portion 726 of the cam to the rocker 704 for the valve 706 to actually be lifted off of its seat, and thus the valve 706 closes or remains closed. The valve train 700 thus provides a lost-motion feature that allows for variable valve actuation (i.e., permits the valve 706 to close at an earlier time than that provided by the profile of the cam 702). The valve train 700 is therefore configured to transmit all of the cam motion to the valve 706, to transmit only a portion of the cam motion to the valve 706, or to transmit none of the cam motion to the valve 706.

Direct Attack Valve Train with Bucket Tappet

FIG. 8 illustrates an exemplary embodiment of a direct attack valve train 800 with a bucket tappet. As shown, the valve train 800 generally includes a cam 802, a valve 806, an adjustable mechanical element 808, and a bucket tappet 852. The adjustable mechanical element 808 includes an actuation system 854 and a bearing element 836. Except as indicated below or as will be apparent to one having ordinary skill in the art, the structure and operation of the components of the valve train 800 are substantially the same as the corresponding components of the valve train 200 described above.

The valve 806 includes a valve head 810 and a valve stem 812 extending vertically from the valve head 810. A valve spring (not shown) holds the valve head 810 securely against a valve seat (not shown) when the valve 806 is in its closed position. Any of a variety of valve springs can be used for this purpose, including, for example, air or gas springs. The valve is an inwardly-opening poppet valve, such that the valve opens by moving inward, towards the engine cylinder.

The tappet 852 is disposed over the valve stem 812 and provides a contact surface for engaging the bearing element 836. In the illustrated embodiment, the tappet 852 is a hollow cylindrical canister that is closed at one end. The adjustable mechanical element 808 is positioned such that the bearing element 836 is disposed between the tappet 852 and the cam 802.

In operation, the cam 802 rotates clockwise as a camshaft, to which it is mounted, is driven by rotation of the engine's crankshaft. When the base circle portion 818 of the cam 802 engages the bearing element 836, the valve train 800 remains in a “fully closed” position in which the cam 802 does not apply sufficient opening force to the bearing element 836 and tappet 852 to overcome the bias of the valve spring, and therefore the valve 806 remains closed.

The actuating portion 826 of the cam 802 engages the bearing element 836 during a portion of the cam's rotation. When the actuation system 854 is in a “locked” configuration, the actuating portion 826 imparts a downward motion to the bearing element 836, resulting in a downward motion of the tappet 852 and valve 806, which lifts the valve 806 off of its seat. In other words, the bearing element 836 can be held between the cam 802 and tappet 852 such that the motion of the valve 806 will substantially follow the profile of the cam 802 according to the geometry of the actuation elements of the valve train.

The valve 806 can be closed before the timing specified by the cam profile by transitioning the actuation system 854 to an “unlocked” configuration. In the unlocked configuration, the actuation system 854 allows the bearing element 836 to be at least partially ejected from between the cam 802 and the tappet 852 by valve train forces. The bearing element 836 can be withdrawn far enough from the cam 802 and the tappet 852 such that insufficient motion is imparted from the actuating portion 826 of the cam to the tappet 852 for the valve 806 to actually be lifted off of its seat, and thus the valve 806 closes or remains closed. The valve train 800 thus provides a lost-motion feature that allows for variable valve actuation (i.e., permits the valve 806 to close at an earlier time than that provided by the profile of the cam 802). The valve train 800 is therefore configured to transmit all of the cam motion to the valve 806, to transmit only a portion of the cam motion to the valve 806, or to transmit none of the cam motion to the valve 806.

Although the invention has been described by reference to specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims. 

What is claimed is:
 1. A lost-motion variable valve actuation system, comprising: a rocker arm having a first rocker pad that engages an engine valve and a second rocker pad; a pushrod having a first end in engagement with the second rocker pad and a second end in engagement with a follower; and an actuation system configured to selectively permit a bearing element to be at least partially ejected from between the follower and a cam to allow the engine valve to close.
 2. The system of claim 1, wherein the follower comprises a cylindrical canister with a closed end that defines a contact surface that engages the bearing element.
 3. The system of claim 1, wherein the follower is configured to rotate about an axis of rotation and wherein the follower comprises a first end having a bore formed therein through which a shaft extends along the axis of rotation and a second end opposite the first end that engages the bearing element.
 4. The system of claim 3, wherein the second end comprises a roller rotatably mounted therein such that the roller engages the bearing element.
 5. The system of claim 3, wherein the second end of the pushrod engages the follower at a location intermediate to the first and second ends of the follower.
 6. The system of claim 3, wherein the pushrod is coupled to the follower by a ball and socket coupling.
 7. The system of claim 1, wherein the engine valve is inwardly-opening.
 8. The system of claim 1, wherein the actuation system has a locked configuration in which the bearing element is maintained between the follower and the cam and an unlocked configuration in which the bearing element can be at least partially ejected from between the follower and the cam.
 9. A lost-motion variable valve actuation system, comprising: a rocker arm having a first rocker pad that engages an engine valve and a second rocker pad; and an actuation system configured to selectively permit a bearing element to be at least partially ejected from between the second rocker pad and a cam to allow the engine valve to close; wherein the rocker arm is configured to rotate about an axis of rotation.
 10. The system of claim 9, wherein the first and second rocker pads are formed at opposed ends of the rocker arm and wherein the axis of rotation is disposed intermediate to the first and second rocker pads.
 11. The system of claim 9, wherein the axis of rotation is disposed at a first end of the rocker arm, the first rocker pad is formed at a second, opposite end of the rocker arm, and the second rocker pad is formed at a location intermediate to the first and second ends of the rocker arm.
 12. The system of claim 9, wherein the second rocker pad comprises a roller rotatably mounted in the rocker arm.
 13. The system of claim 9, wherein the engine valve is inwardly-opening.
 14. The system of claim 9, wherein the actuation system has a locked configuration in which the bearing element is maintained between the rocker arm and the cam and an unlocked configuration in which the bearing element can be at least partially ejected from between the rocker arm and the cam. 